Substituted dihydropyridines are known to be useful for reducing blood pressure, effecting dilation of the coronary vessels, and preventing urospasms. Typical of such substituted dihydropyridines are those disclosed in U.S. Pat. Nos. 3,923,818; 3,905,970; 4,044,141; 4,237,137; and, 4,285,955. The substituted dihydropyridines disclosed in these patents do not include bridged ring structures.
Weller et al., [J. Org. Chem., 48, pp. 3061-7 (1983)] disclose 1'-methylspiro[benzofuran-3(2H),4'-piperidine] as a substructure of morphine which is an early intermediate in a general synthesis of morphine but not possessing exceptional analgesic activity. Weller et al. also teach the preparation of spiro [benzofuran-3(2H),4'-(1'H)-pyridines as potential intermediates in a synthesis of morphine but no biological activity of these compounds is reported.
Goldman [Angew. Chem. Int. Ed. Engl., 20, pp. 779-780 (1981)] teaches the preparation of spiro[benzothiophene-1-oxide,4-pyridines] as an intermediate in the preparation of 4,4-disubstituted 1,4-dihydropyridines.